feat: verb subtype + updateRelation + requireSubtype enforcement

Brings verbs to first-class parity with nouns. The 7.29.0 subtype primitive
shipped for entities only; this release ships the symmetric verb mirror plus
the enforcement layer for ensuring every entity AND every relationship has
both type AND subtype.

Layer V1 — verb subtype mirror
- HNSWVerbWithMetadata.subtype + STANDARD_VERB_FIELDS set + resolveVerbField()
- Relation<T>.subtype, RelateParams<T>.subtype, UpdateRelationParams<T> extended,
  GetRelationsParams.subtype, GraphConstraints.subtype (for find connected)
- relate() persists subtype on verbMetadata + GraphVerb + transaction ops
- getRelations({ type, subtype }) fast-path filter with set membership
- find({ connected: { via, subtype, depth } }) traversal filter (depth-1 on
  the JS path; explicit error on depth > 1 pointing at Cortex native)
- verbsToRelations + storage destructure sites surface subtype to top-level
- All three graph-index fast-path queries (getVerbsBySource/ByTarget) enrich
  with subtype from metadata

Layer V2 — updateRelation() closes a pre-7.30 gap
- New first-class verb update method (parallel to update() for nouns)
- Changes subtype/type/weight/confidence/data/metadata in place
- Re-indexes in graph adjacency when verb type changes; id preserved
- validateUpdateRelationParams enforces id + at-least-one-field-to-update

Layer V3 — verb subtype storage rollup
- verbSubtypeCountsByType: Map<number, Map<string, number>> on BaseStorage
- verbSubtypeByIdCache for self-heal during update/delete
- incrementVerbSubtypeCount + decrementVerbSubtypeCount maintain state
- loadVerbSubtypeStatistics + saveVerbSubtypeStatistics persist to
  _system/verb-subtype-statistics.json (mirrors noun-side shape)
- rebuildVerbSubtypeCounts for poison recovery / explicit repair
- getVerbSubtypeCountsByType accessor for the public counts API
- Wired into init() / flushCounts() / saveVerbMetadata / deleteVerbMetadata

Layer V4 — verb counts API + relationshipSubtypesOf
- brain.counts.byRelationshipSubtype(verb, subtype?) — O(1) breakdown or point
- brain.counts.topRelationshipSubtypes(verb, n) — top N by count
- brain.relationshipSubtypesOf(verb) — sorted distinct subtypes

Layer V5 — migrateField extended to verbs
- New entityKind?: 'noun' | 'verb' | 'both' option (default 'noun')
- Mirror verb iteration via storage.getVerbs() with same path semantics
- verbToRelationLike + buildRelationMigrationUpdate helpers project the
  storage verb shape onto the Entity<T>-shaped surface readPath understands
- Routes through new updateRelation() for the verb-side rewrite

Enforcement (opt-in in 7.30, default in 8.0)
- brain.requireSubtype(type, options) — unified API for NounType OR VerbType.
  Registers per-type rules with optional values whitelist; composes with the
  brain-wide flag.
- new Brainy({ requireSubtype: true }) — brain-wide strict mode. Every public
  write path validates the pairing guarantee.
- { except: [NounType.Thing, ...] } form for catch-all type exemptions
- Atomic-fail semantics on addMany / relateMany — pre-validate every item
  before any storage write, throw on first failure with item index
- Per-type rules + brain-wide flag both throw with descriptive messages
- VFS infrastructure bypass via metadata.isVFSEntity / isVFS markers so
  brain's own VFS writes don't get rejected when strict mode is on

VFS labeling — concrete subtypes for infrastructure entities
- VFS root: NounType.Collection + subtype: 'vfs-root' (was bare Collection)
- VFS directories: subtype: 'vfs-directory'
- VFS files: subtype: 'vfs-file' (NounType still mime-based)
- VFS containment edges: VerbType.Contains + subtype: 'vfs-contains'
- Lets consumers cleanly enumerate VFS state via find({ subtype: 'vfs-file' })
  and distinguish Brainy's VFS Collections from user-created Collections

Docs
- docs/guides/subtypes-and-facets.md extended with Layer V (Verbs) section +
  Enforcement section. New full reference at the bottom split into Layer 1
  (nouns), Layer V (verbs), Layer 2 (facets), Layer 3 (migration), Enforcement.
- docs/api/README.md adds updateRelation(), getRelations({ subtype }), the
  three verb-side counts methods, requireSubtype(), and the brain-wide
  constructor option. relate() params include subtype.
- docs/DATA_MODEL.md adds a Subtype-for-VerbType section + STANDARD_VERB_FIELDS
- docs/architecture/finite-type-system.md extends Principle 1a to verbs
- docs/QUERY_OPERATORS.md adds a verb-subtype filter section covering
  getRelations and find({connected, subtype}) traversal
- README.md "Subtypes" section now shows both noun + verb in one example +
  the enforcement APIs
- RELEASES.md v7.30.0 entry with the full noun/verb capability parity matrix

Tests
- tests/integration/verb-subtype-and-enforcement.test.ts — 30 new tests
  covering V1 round-trips, V1 set membership, updateRelation in place,
  updateRelation preservation, V2 counts breakdown + point + topN + distinct,
  V2 decrements on unrelate, V2 re-routes on updateRelation, V3 depth-1
  traversal filter, V3 depth>1 explicit error, V4 verb migration, V4 both
  entity kinds, V4 readBoth preservation, V5 per-type required rejection,
  V5 vocabulary rejection, V5 on-vocab acceptance, V5 verb-side enforcement,
  V5 addMany atomic-fail, V5 relateMany atomic-fail, V5 update enforcement,
  V5 updateRelation enforcement, V5 brain-wide strict mode, V5 except clause.

Verification
- Unit suite: 1468/1468 passing
- Noun subtype integration (7.29 carryover): 26/26 passing
- Verb subtype + enforcement integration: 30/30 passing
- Type-check: clean
- Build: clean
- Public closed-source reference audit: clean

Internal 8.0 spec
- .strategy/BRAINY-8.0-SUBTYPE-CONTRACT.md (gitignored, not in npm artifact)
  documents the contract upgrade Cortex 3.0 implements against: required-by-
  default subtype, SubtypeRegistry typing hook, native simplification,
  multi-hop traversal native fast path, brain.fillSubtypes() migration helper.
  Coordinated via PLATFORM-HANDOFF rows CTX-SUBTYPE-PARITY-V2 (7.30 parallel
  work) and CTX-SUBTYPE-8.0-CONTRACT (8.0 spec).

src/vfs/VirtualFileSystem.ts

@@ -245,6 +245,7 @@ export class VirtualFileSystem implements IVirtualFileSystem {
         id: rootId,  // Fixed ID - storage ensures uniqueness
         data: '/',
         type: NounType.Collection,
+        subtype: 'vfs-root',  // Standard subtype for the VFS root collection (7.30+)
         metadata: this.getRootMetadata()
       })
 
@@ -511,6 +512,7 @@ export class VirtualFileSystem implements IVirtualFileSystem {
       const entity = await this.brain.add({
         data: embeddingData,  // Always provide string for embeddings
         type: this.getFileNounType(mimeType),
+        subtype: 'vfs-file',  // Standard subtype for VFS file entities (7.30+)
         metadata
       })
 
@@ -519,6 +521,7 @@ export class VirtualFileSystem implements IVirtualFileSystem {
         from: parentId,
         to: entity,
         type: VerbType.Contains,
+        subtype: 'vfs-contains',  // Standard subtype for VFS containment edges (7.30+)
         metadata: { isVFS: true }  // Mark as VFS relationship
       })
 
@@ -890,6 +893,7 @@ export class VirtualFileSystem implements IVirtualFileSystem {
       const entity = await this.brain.add({
         data: path,  // Directory path as string content
         type: NounType.Collection,
+        subtype: 'vfs-directory',  // Standard subtype for VFS directory entities (7.30+)
         metadata
       })